The cleanout mechanism in a known bowl-mill crusher (Au-fbereitungs-Technik 12 [1971], 9, 542-43) consists of two arms secured to the grinding-bowl support that sweep over the horizontal bottom of the air box at each revolution. Coarse material that arrives in the air box from the grinding area by way of the nozzle ring is emptied into the removal container through an extraction opening in the bottom of the air box. To protect the cleanout arms from damage or destruction by coarse particles, the arms are loosely articulated to the grinding-bowl support and can roll over the particles. An articulation of this type is subject to malfunction. Furthermore, larger quantities of ground material arrive in the air box from the grinding area when the supply of air to the grinder is suddenly discontinued in the event of an emergency turnoff. The known cleanout arms, which sweep the horizontal bottom of the air box, are then no longer able to remove the ground material out of the air box rapidly enough.